A team of astronomers has discovered half a dozen exocomets, which may be as common as exoplanets orbiting other stars, researchers said Tuesday. The research, presented Monday at the American Astronomical Society meeting in Long Beach, could provide tantalizing clues about the growth and evolution of alien planetary systems. “We've found essentially the leftover building blocks of planetary systems,” said UC Berkeley astronomer Barry Welsh, who presented the research. Comets around other stars may seem hard to find, given that exoplanets are already a challenge and comets are much smaller -- typically 3 to 13 miles wide.

A pair of NASA orbiters has given scientists their highest-fidelity look at the moon, a leap that could help explain the evolution of the solar system's rocky planets, including Earth. Scientists announced the first results Wednesday from the $496-million GRAIL mission, the Gravity Recovery and Interior Laboratory, which consists of two washing-machine-size spacecraft that operate in tandem. GRAIL lifted off from Cape Canaveral, Fla., in September 2011, and the spacecraft are now circling the moon, studying its structure, surface and composition.

December 3, 2012 | By Amy Hubbard, This post has been corrected. See the note below for details.

Voyager 1 is this close to interstellar space -- probably. On its way out of our solar system, the spacecraft has stumbled across a surprise: a "magnetic highway" that represents a brand-new, unexpected layer between here and out there. This new layer, scientists said Monday morning, provides hints of interstellar space. Edward Stone, Voyager project scientist, told reporters at the American Geophysical Union meeting in San Francisco on Monday that particles were "zipping in and out on this magnetic highway.

Voyager 1, the spacecraft famous for beaming back striking photos of Jupiter, Saturn and their moons more than 30 years ago, has made still another surprising discovery: the existence of an unexpected zone at the very edge of the solar system. It had been thought that the NASA probe was already passing through the outermost section of the solar system on its way toward the heliopause - the boundary where the solar wind ends and interstellar space begins. For that reason, the existence of yet another district at our cosmic neighborhood's edge was completely unexpected, said Stamatios Krimigis, a solar physicist at the Johns Hopkins Applied Physics Laboratory in Laurel, Md., and leader of the team that operates Voyager's low-energy charged particle instrument.

Over the last few weeks, astronomers announced not one but two extraordinary discoveries in the ongoing search for planets orbiting stars beyond the sun. The first was a world about the size of Neptune, 5,000 light-years away, whirling around in a solar system with four stars. It's something like Luke Skywalker's home world of Tatooine in the "Star Wars" movies, except that fictional planet sported only two suns. The second was an Earth-size planet right next door in the Alpha Centauri system - three stars that orbit one another not thousands or hundreds but a mere four light-years from our solar system.

The giant asteroid Vesta, sometimes known as a proto-planet, has a surface unlike any other airless body previously observed. While Earth's moon and other airless bodies are generally a relatively uniform gray, Vesta's bright background is streaked with large amounts of a much darker substance. New results from the Dawn probe indicate that the black material is largely carbon that has been deposited by other, smaller asteroids. The moon and other airless bodies like it exhibit a form of weathering, even though the lack of an atmosphere prevents weather as we know it. Over billions of years, the bodies have become gray as a result of exposure to the solar wind and bombardment by micrometeorites.

When Yale astronomer Megan Schwamb announced the discovery of a distant planet at an astronomy meeting in Reno this week, the stargazing world was left agog. The oddball Neptune-sized gas giant she described was the first ever seen in a solar system of not one, not two, but four gravitationally connected stars. It was like the fictional planet Tatooine of "Star Wars" fame, but with two extra, distant suns. The planet orbits one pair of stars (which are rotating around each other)

Analyzing grains of soil collected from three Apollo lunar missions, geochemists have figured out that the hydrogen in trace amounts of water on the moon's surface probably came from solar wind, the outflow of positively-charged hydrogen from the sun. For decades, scientists didn't find much hydrogen in the lunar samples that had been returned to Earth, said Yan Liu, a research professor at the University of Tennessee and lead author of the lunar...

Re "Ready for a real star trek," Sept. 8 Thank you for your article on Voyager 1's imminent departure from our solar system. While Jet Propulsion Laboratory scientists are now focused on the spacecraft's passage into interstellar space, the greatest legacy of the Voyager 1 and 2 missions is the stunning images they have captured - of Jupiter's Great Red Spot, the Jovian moon Io's erupting volcanoes, Saturn's rings, Uranus and Neptune....